symbols: use correct max value

xkb_level_index_t was initially uint16_t, now it's 32.

Signed-off-by: Ran Benita <ran234@gmail.com>
symbols: improve FindKeyForSymbol()

A bit more involved, but can short circuit.

Signed-off-by: Ran Benita <ran234@gmail.com>
keymap: rename XkbKeyGroupWidth to XkbKeyNumLevels

The "width" terminology comes from the group*width+level layout of the
keysyms in a key, as used in the old implementations. We don't keep all
the keysyms of a key in one array so change it to a more accurate name.

Signed-off-by: Ran Benita <ran234@gmail.com>